Specimen stage and holder assembly for electron microscope

ABSTRACT

In an electron beam apparatus, two stage plates are nested one within the other and are slidable on a common reference surface to provide X-Y motion for scanning a specimen positioned on the optical axis of the apparatus. The specimen holder is mounted on a carriage which is carried by one of the stage plates and is movable relative to the stage plate along one axis. The specimen stage and holder assembly may be constructed to tilt the specimen in any direction about the optical axis.

United States Patent Lucas 1 Feb. 15, 1972 [54] SPECIMEN STAGE AND HOLDER ASSEMBLY FOR ELECTRON MICROSCOPE [72] Inventor: Jeffrey 11. Lucas, Rickling, NR. Saffron, Walden, Essex, England [73] Assignee: Associated Electrical Industries Limited,

Stanhope Gate, London, England [22] Filed: Aug. 19, 1969 21 J Appl. No.: 851,172

[30] Foreign Application Priority Data Aug. 30, 1968 Great Britain ..41,572/68 [52] U.S. Cl ..250/49.5 B

[51] Int. Cl ..H01j 37/20 [58] Field of Search ..250/49.5 A, 49.5 B

[56] References Cited UNITED STATES PATENTS 2,264,210 11/1941 Krause ..250/49.5 B 2,380,209 7/1945 Bachman et al.... .....250/49.5 B 2,499,019 2/1950 Dornfeld ..250/49.5 B 2,602,899 7/1952 Page ..250/49.5 B 3,488,493 1/1970 Mills..... ..250/49.5 B

Primary Examiner-Anthony L. Birch Attorney-Watts, Hotfrnann, Fisher & Heinke [57] ABSTRACT In an electron beam apparatus, two stage plates are nested one within the other and are slidable on a common reference surface to provide X-Y motion for scanning a specimen positioned on the optical axis of the apparatus. The specimen holder is mounted on a carriage which is carried by one of the stage plates and is movable relative to the stage plate along one axis. The specimen stage and holder assembly may be constructed to tilt the specimen in any direction about the optical axis.

17 Claims, 8 Drawing Figures PATENTEUFEB v 5 I972 SHEET 1 OF 3 INVENTOR. JEFFREY HAEx EY LUCAS ATTOENEYE.

mam/ 4 PATENTEDFEB 15 1972 SHEET 2 OF 3 INVENTOR. JEFF/'xfiY HARVEY Lucas BY 9%, $14M W ATTOENEYfi' PATENTEBFEB '1 5 I972 SHEET 3 BF 3 INVENTOR. JEFFREY HARVEY LUCAS ATTOENE /5.

SUMMARY OF THE INVENTION The present invention relates generally to electron microscopes, and more specifically ,to a new specimen stage and holder assembly.

An object of the present invention is to provide an electron microscope specimen stage and holder assembly which is capable of positioning a specimen in the electron beam with a high degree ofaccuracy.

Another object of the present invention is to provide a highly adaptable specimen stage and holder assembly for an electron microscope which is characterized by versatility of movement, whereby several different types of scans through one or more specimens can be made.

A further object of the present invention is to provide an electron microscope specimen stage and holder assembly which enables the positioning of one or more specimens in the electron beam to be varied in such a manner as to allow different zones of each specimen to be scanned.

Another object of the present invention is to provide a new specimen stage and holder assembly characterized by nested stage plates movable on a common reference surface along orthogonal axes.

Still another object of the present invention is to provide an electron microscope specimen stage and holder assembly as described in any of the preceding paragraphs which is constructed to enable the specimen to be tilted in any direction about the optical axis.

A further object of the present invention is to provide an electron microscope specimen stage and holder assembly which is capable of supporting a multiple number of specimens and which permits accurately repeatable focal settings for sequential specimens to be made.

Yet another object of the present invention is to provide an electron microscope specimen stage and holder assembly characterized by mechanical stability and a compact construction.

In a preferred embodiment of the present invention, the new specimen stage is comprised of two stage plates which provide the X-Y motion for scanning over a specimen positioned on the optical axis of an electron microscope. The specimen holder is mounted on a carriage which is independently movable on one of the stage plates along one of the orthogonal axes to obtain accurate specimen positioning and to facilitate loading.

A featured aspect of the present invention resides in a nested arrangement of the two main stage plates. In a preferred form of the invention, one of the stage plates is in the general form of a rectangular frame and is movable on a reference surface along the X-axis. The second main stage plate is disposed within the first one and rests on the same reference surface for movement along the Y-axis. This preferred arrangement in which the nested stage plates are movable on a common surface provides good mechanical stability and a compact construction.

Preferably, the specimen holder is adapted to carry several specimens simultaneously. In one embodiment of the invention, the specimen holder has a plurality of spaced stations and is movable so that the specimens located at the stations can be selected in any sequence for examination. In another embodiment, the specimen holder is provided with a slit in which seri- 31 sections can be mounted. The controlled movements of the stage plates and carriage on which the specimen holder is mounted permits the specimens to be scanned in continuous sequence as well as permitting a zigzag scan over all of the sections.

According to another feature of the invention, the specimen holder is constructed to mount a specimen so that it can be tilted in any direction about the optical axis so as to vary the direction in which a specimen is examined. The tilting movement permits alignment of features in depth in specimens with LII the electron beam passing along the optical axis. and also permits alignment of particular planes in crystallographic examinations.

Other objects, features and advantages of the invention will be had by reference to the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a diagrammatic, vertical section showing the general arrangement of an electron microscope;

FIG. 2 is a perspective view with portions cut away of a specimen stage and holder assembly embodying the present invention;

FIG. 3 is an enlarged, perspective view of a preferred specimen holder;

FIG. 4 is an enlarged perspective view of another preferred specimen holder;

FIG. 5 is an enlarged, perspective view with portions cut away of still another preferred specimen holder;

FIG. 6 is an'exploded, enlarged view of a portion of the specimen holder shown in FIG. 5;

FIG. 7 is an enlarged, fragmentary cross-sectional view of a portion of the specimen holder shown in FIG. 5; and,

FIG. 8 is an enlarged, fragmentary view of the new specimen stage embodying the specimen holder of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. I, the general arrangement of the illustrated electron microscope is shown to include a casing 10 having ducts 12, 13 connected to a vacuum pump (not shown). An electron gun 14 is provided at the upper end of the microscope and is positioned to project an electron beam downwardly. Passing downwardly from the electron gun 14, the arrangement also includes a condenser lens 15, a specimen stage 16, an objective lens 17 and a projector lens 18. A fluorescent screen 19 and binocular eye pieces 20 are provided at the bottom of the casing 10. As generally set forth above, the present invention is concerned with a new and improved specimen stage 16.

Referring now to FIG. 2, the specimen stage of this invention is shown to comprise a cup-shaped support base 25 which includes a peripheral rim 26 and a flat reference surface 27 having an opening (not shown) through which electron beams pass along the optical axis OO. Two main stage plates 28, 29 which provide X-Y motion for scanning over a specimen held on the optical axis O-O rest directly upon the flat surface 27.

The stage plate 28 has the general form of a rectangular frame having extensions 30 (only one of which is shown) projecting from opposite sides. Guide rollers 31 connected to the surface 27 of the support base 25 engage the sides of the extensions 30 to guide the stage plate 28 for movement along the X-axis. Movement can be imparted to the stage plate 28 in any suitable manner, such as by a threaded shaft 32 which extends through the support base rim 26 into engagement with one of the extensions 30. A suitable vacuum seal (not shown) is provided around the rod 32.

The main stage plate 29 is located within the plate 28 and is guided for movement along the Y-axis by rollers 37 which are carried by the plate 28. The stage plate 29 is adapted to be moved along the Y-axis in any suitable manner, such as by a threaded rod 38 which includes a flexible shaft portion 39 to accommodate movement of the stage plates along the X-axis. The rod 38 extends through the rim 26 of the support base 25 and a suitable vacuumseal (not shown) is provided around the rod.

The stage plate 29 is formed with a dovetail slideway 40 which extends parallel to the direction of movement of the plate. The member 29 is also formed with a raised ledge 41 which is parallel to the slideway 40 and which has an upper surface that is machined flat. The upper surface of the ledge 41 presents an accurate register at a fixed height in the objective lens pole gap.

A carriage 45 is mounted on the stage plate 29 and is movable along the slideway 40. As shown in FIG. 8, the carriage 45 is moved along the slideway 40 by a pinion 46 which engages a rack 47 on the undersurface of the carriage. The pinion 46 is carried on a shaft 48 which is connected by a coupling 49 to a flexible shaft 50 extending through a vacuum seal in the rim 26. The coupling 49 and the flexible shaft 50 allow movement of the stage plates 28, 29 along the X-Y axes. In the illustrated arrangement, the flexible shaft 50 is connected to a drive shaft 51 positioned externally of the casing (FIG. 2). The shaft 51 can be operated by hand or by a suitable motor drive (not shown). An indicator 52 is mounted on the control shaft 51 in association with a suitable scale 53 for use in controlling the scanning of specimens in a manner to be more specifically described,

The carriage 45 includes a portion 56 extending laterally from the slideway 40 over the raised ledge 41 of the stage plate 29. A slot 57 is milled in the undersurface of the carriage portion 56 parallel to the ledge 41 and opens downwardly. A specimen holder 58, which is shown in greater detail in FIG. 3, is mounted within the carriage slot 57. The specimen holder 58 includes a shank portion 59 which is held firmly within the carriage slot 57 by a latch (not shown). A leaf spring (also not shown) mounted within the slot 57 presses the specimen holder 58 downwardly against the flat surface of the raised ledge 41. By pressing the specimen holder against the ledge 41, accurately repeatable focal settings for sequential specimens can be made, thereby providing for accurate calibration of instrumental magnification. Another feature of the described construction resides in its mechanical stability. The holder 58 is constructed so that for any selected specimen grid hole, the holder bridges across the clearance hole in the stage plate 29 and is thus held firmly in position. Many prior art specimen holders have a cantilever support and are susceptible to mechanical resonance.

As shown in FIG. 3, the specimen holder 58 contains six specimen grids 65 so that six specimens can be loaded into the holder and examined successively. Each specimen grid 65 is mounted within a hole in the holder and is retained in place by a clip 66. It will be seen that operation of the control shaft 51 is such that the carriage 45 can be moved to select any one of the specimen grids to be aligned with the optical axis. The X-Y movements of the stage plates 28, 29 permit scanning of one complete grid area before selection ofthe next grid and so on. When using the specimen holder 58, the scale 53 is preferably calibrated to indicate the positioning of the holder, whereby the microscope operator can tell which of the particular grids is aligned with the optical axis.

The illustrated arrangement of FIG. 2 also facilitates a simplified operation of loading several specimens into the stage. This is accomplished by turning the control shaft 51 so that the carriage 45 is moved radially outwardly along the Y-axis to a location adjacent a port 75 through the rim 26 of the support base 25. The normally sealed port 75 is adapted to be opened so that specimen holders can be conveniently loaded and unloaded from the carriage 45.

FIG. 4 illustrates a modified specimen holder 76 wherein the several grid holes of the previously described holder 58 are replaced by a single slot 77. The slot 77 enables serially related specimens to be mounted adjacent to each other along the length of the slot so that they can be examined one after the other without interruption of the field of view by portions of the holder. When using the holder 76, the control scale 53 (FIG. 2) is preferably changed from an indication of separate grid locations to a continuous millimetric calibration so that a continuous scan through all ofthe specimens in the slot 77 can be made. If desired, a zigzag scan can be made to cover the whole area of the specimens exposed in the slot by the use of the control shaft 51 and the X-stage control shaft 32.

As generally explained above, it is desirable in many types of examinations to tilt the specimen about the optical axis of the microscope, such as when it is required to align features in depth in specimens with the electron beam passing along the optical axis or when it is required to align particular planes in crystallographic examinations. FIGS. 5-8 show a specimen holder construction 80 which permits such tilting movement.

The holder 80 is comprised of a bar 81 having a rectangular shank 82. A small spherical member 83, which contains a grid 84 suitably mounted within a hole through the member, is clamped between the bar 81 and an overlying plate 85 so that the member 83 can be rotated to permit angular positioning of the specimen. As shown most clearly in FIG. 7, the spherical member 83 rests on a seating surface 86 formed around a hole 87 through the bar 81 and is engaged by a similar seating surface 88 formed around a hole 89 through the retaining plate 85.

The spherical member 83 is rotated by arms 90, 91 which are pivotally mounted between their ends at 92, 93, respectively, on the bar 81. The arm has a ball-shaped end or probe 94 which is engaged within a recess 95 of a seating or boss 96 extending from the spherical member 83. The arm 91 has a similar ball-shaped end or probe 97 engageable within a recess of a seating boss 98 extending from the member 83. The seating surface or bosses 96, 98 are positioned at right angles to each other so that the specimen-carrying sphere 83 can be tilted in any direction by actuation of the pivotally mounted arms 90, 91.

The specimen holder 80 is adapted to be retained within the slot 57 of the carriage 45 in the same manner previously described in connection with the specimen holder 58. When the specimen holder 80 has been inserted into the carriage 45, the end 100 of the arm 90 is automatically engaged by a lever 102 which is pivotally mounted between its ends on the carriage. The end 101 of the arm 91 is similarly engaged by a pivotal lever 103 which is mounted in the carriage 45. The levers 102, 103 are operated by cams 105 (only one of which is shown in FIG. 8) and are automatically engageable with the cams when the carriage 45 is moved to align the specimen-carrying member 83 with the optical axis. The cam 105 are mounted on shafts 106, 107 which are flexibly connected to control shafts 108, 109, respectively of an externally mounted control 110, Each of the control shafts 108, 109 carries a sector gear 111 which is actuated by a suitable motor 112. Each control shaft 108, 109 is further coupled to indicating 113, 114, respectively, for indicating the tilt of the spherical member 83.

Although forming no part of the present invention, the stage as illustrated in FIG. 2 includes an aperture rod which extends through a vacuum seal in the rim 26 of the base support 25 and is provided with a series of irises 121 of different diameters so that by moving the rod 120 longitudinally, different iris apertures can be brought into alignment with the optical axis 0-0. A decontaminator assembly 122 includes blades 123 is also shown as extending through a vacuum seal in the rim 26.

Many modifications and variations of the invention will be apparent to those skilled in the art in light of the foregoing detailed disclosure. Therefore, it is to be understood that, within the scope of the appended claims, the invention can be practiced otherwise than as specifically shown and described.

What is claimed is:

1. In an electron beam apparatus including structure defining a flat reference surface having an opening through which electron beams pass along an optical axis, an improved specimen stage and holder assembly comprising nested stage plates, each having portions in intimate physical contact with and movable on said reference surface along orthogonal axes, means for moving each of said plates, a specimen holder, and means mounting said specimen holder on one of said plates.

2. Apparatus as claimed in claim 1 wherein said mounting means comprises a carriage mounted on said one plate for rectilinear movement, and means for moving said carriage.

3. Apparatus as claimed in claim 2 wherein said specimen holder includes a plurality of specimen mounting stations, and wherein said carriage is movable to permit said stations to be aligned on said optical axis in any desired sequence.

4. Apparatus as claimed in claim 3 wherein said carriage moving means includes means for indicating the selected specimen station aligned on the optical axis.

5. Apparatus as claimed in claim 2 wherein said specimen holder includes a slit adapted to mount serially related specimens.

6. Apparatus as claimed in claim 1 wherein said specimen holder includes means for tilting a mounted specimen about said optical axis.

7. Apparatus as claimed in claim 6 wherein said tilting means comprises a spherical member containing a specimen grid, means mounting said member for universal tilting movement, and means engageable with said member for tilting it.

8. in an electron beam apparatus including structure defining a fiat reference surface having an opening through which electron beams pass along an optical axis, an improved specimen stage and holder assembly comprising a first stage plate slidably mounted on andhaving portions in intimate physical contact with said reference surface, means guiding said first plate for movement along a first axis, a second stage plate slidably mounted on and having portions in intimate physical contact with said reference surface and movable with said first plate, means guiding said second plate for movement along a second axis transverse to said first axis, means for moving said plates, a specimen holder, and means mounting said holder on one of said plates.

9. Apparatus as claimed in claim 8 wherein said first plate comprises a frame, and wherein said second plate is disposed within said frame on said reference surface.

10. In an electron beam apparatus including structure defining a flat reference surface have an opening through which electron beams pass along an optical axis, an improved specimen stage and holder assembly comprising a first stage plate slidable on and having portions in intimate physical contact with said reference surface, means guiding said first plate for movement along a first axis, a second stage plate slidable on and having portions in intimate physical contact with said reference surface and movable with said first plate, means guiding said second plate for movement along an axis transverse to said first axis, means for moving said plates, a carriage slidably mounted on said second plate for movement along said second axis,v means for moving said carriage, and a specimen holder mounted on said carriage.

11. Apparatus as claimed in claim 10 wherein said second plate includes a flat surface parallel to the path of carriage movement, and wherein said specimen holder is slidable on said flat surface.

12. Apparatus as claimed in claim 11 wherein said specimen holder includes a plurality of specimen mounting stations adapted to be selectively aligned on said optical axis by movement of said carriage.

13. Apparatus as claimed in claim 11 wherein said specimen holder includes a slit adapted to mount serially related specimens.

14. Apparatus as claimed in claim 11 wherein said specimen holder includes means for tilting a mounted specimen about said optical axis.

15. In an electron beam apparatus including structure defining a flat reference surface having an opening through which electron beams pass along an optical axis, an improved specimen stage and holder assembly comprising:

a. stage plates movable along orthogonal axes, on said reference surface and having portions in intimate physical contact therewith;

b. said holder including:

i. a spherical specimen mounting member,

ii. structure mounting said spherical member for universal tilting movement,

iii. means engageable with said spherical members for imparting universal tilting movement,

c. and means engageable with said last-mentioned means for operating the same. 16. Apparatus as claimed in claim 15 wherein said stage plates are nested one within another and are each movable on said reference surface.

17. Apparatus as claimed in claim 15 wherein said holder mounting means comprises a carriage slidable on said one plate. 

1. In an electron beam apparatus including structure defining a flat reference surface having an opening through which electron beams pass along an optical axis, an improved specimen stage and holder assembly comprising nested stage plates, each having portions in intimate physical contact with and movable on said reference surface along orthogonal axes, means for moving each of said plates, a specimen holder, and means mounting said specimen holder on one of said plates.
 2. Apparatus as claimed in claim 1 wherein said mounting means comprises a carriage mounted on said one plate for rectilinear movement, and means for moving said carriage.
 3. Apparatus as claimed in claim 2 wherein said specimen holder includes a plurality of specimen mounting stations, and wherein said carriage is movable to permit said stations to be aligned on said optical axis in any desired sequence.
 4. Apparatus as claimed in claim 3 wherein said carriage moving means includes means for indicating the selected specimen station aligned on the optical axis.
 5. Apparatus as claimed in claim 2 wherein said specimen holder includes a slit adapted to mount serially related specimens.
 6. Apparatus as claimed in claim 1 wherein said specimen holder includes means for tilting a mounted specimen about said optical axis.
 7. Apparatus as claimed in claim 6 wherein said tilting means comprises a spherical member containing a specimen grid, means mounting said member for universal tilting movement, and means engageable with said member for tilting it.
 8. In an electron beam apparatus including structure defining a flat reference surface having an opening through which electron beams pass along an optical axis, an improved specimen stage and holder assembly comprising a first stage plate slidably mounted on and having portions in intimate physical contact with said reference surface, means guiding said first plate for movement along a first axis, a second stage plate slidably mounted on and having portions in intimate physical contact with said reference surface and movable with said first plate, means guiding said second plate for movement along a second axis transverse to said first axis, means for moving said plates, a specimen holder, and means mounting said holder on one of said plates.
 9. Apparatus as claimed in claim 8 wherein said first plate comprises a frame, and wherein said second plate is disposed within said frame on said reference surface.
 10. In an electron beam apparatus including structure defining a flat reference surface have an opening through which electron beams pass along an optical axis, an improved specimen stage and holder assembly comprising a first stage plate slidable on and having portions in intimate physical contact with said reference surface, means guiding said first plate for movement along a first axis, a second stage plate slidable on and having portions in intimate physical contact with said reference surface and movable with said first plate, means guiding said second plate for movement along an axis transverse to said first axis, means for moving said plates, a carriage slidably mounted on said second plate for movement along said second axis, means for moving said carriage, and a specimen holder mounted on said carriage.
 11. Apparatus as claimed in claim 10 wherein said second plate includes a flat surface parallel to the path of carriage movement, and wherein said specimen holder is slidable on said flat surface.
 12. Apparatus as claimed in claim 11 wherein said specImen holder includes a plurality of specimen mounting stations adapted to be selectively aligned on said optical axis by movement of said carriage.
 13. Apparatus as claimed in claim 11 wherein said specimen holder includes a slit adapted to mount serially related specimens.
 14. Apparatus as claimed in claim 11 wherein said specimen holder includes means for tilting a mounted specimen about said optical axis.
 15. In an electron beam apparatus including structure defining a flat reference surface having an opening through which electron beams pass along an optical axis, an improved specimen stage and holder assembly comprising: a. stage plates movable along orthogonal axes, on said reference surface and having portions in intimate physical contact therewith; b. said holder including: i. a spherical specimen mounting member, ii. structure mounting said spherical member for universal tilting movement, iii. means engageable with said spherical members for imparting universal tilting movement, c. and means engageable with said last-mentioned means for operating the same.
 16. Apparatus as claimed in claim 15 wherein said stage plates are nested one within another and are each movable on said reference surface.
 17. Apparatus as claimed in claim 15 wherein said holder mounting means comprises a carriage slidable on said one plate. 